login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A065930 (x,y) = (a(n),a(n+1)) are the solutions of (t(x)+t(y))/(1+xy)) = t(4) = 10, where t(n) denotes the n-th triangular number t(n) = n(n+1)/2. 0
4, 79, 1575, 31420, 626824, 12505059, 249474355, 4976982040, 99290166444, 1980826346839, 39517236770335, 788363909059860, 15727760944426864, 313766854979477419, 6259609338645121515, 124878419917922952880 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..15.

J.-P. Ehrmann et al., Problem POLYA002, Integer pairs (x,y) for which (x^2+y^2)/(1+pxy) is an integer.

FORMULA

a(n) = 2t(m)a(n-1)-a(n-2)-1, a(0) = m, a(1) = m^3+m^2-1 with m = 4.

G.f.: (5x-4)/((1-20x+x^2)(x-1)).

MAPLE

g := (5*x-4)/(1-20*x+x^2)/(x-1): s := series(g, x, 40): for i from 0 to 30 do printf(`%d, `, coeff(s, x, i)) od: # James A. Sellers, Feb 11 2002

CROSSREFS

Cf. A000217 (triangular numbers).

Sequence in context: A215843 A048957 A006425 * A018807 A216410 A125710

Adjacent sequences:  A065927 A065928 A065929 * A065931 A065932 A065933

KEYWORD

easy,nonn

AUTHOR

Floor van Lamoen, Nov 29 2001

EXTENSIONS

More terms from James A. Sellers, Feb 11 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 5 03:12 EDT 2020. Contains 334828 sequences. (Running on oeis4.)